CAPE TOWN, South Africa (AP) - The South African government will press ahead with plans to sell just over 51 tons of ivory to China and Japan under a special exemption to the international ban on the trade.

The Convention on International Trade in Endangered Species ruled last year that Botswana, Namibia, South Africa and Zimbabwe would be able to make a one-off sale of 108 tons of government stocks.

Some environmentalists and African countries with dwindling elephant populations fear that it might encourage smuggling and poaching.

South African wildlife experts visited the two nations in September and said they were satisfied that both countries would meet the stringent conditions set by the convention and would not reexport ivory to supply the black market.

In a statement Thursday, the environment ministry said that it would now begin "preparations for the sale."

Ivory trade was banned globally in 1989, but reviving elephant populations allowed African countries to make a one-time sale a decade later to Japan, the only country which had previously won the right to import.

In July, the convention said that China should also be allowed to bid for the ivory at auction later this year as it had dramatically improved its enforcement of ivory rules.

There was opposition to China's inclusion in the auction from Ghana, Kenya and Australia, as well as some environmentalists.

The Washington-based Environmental Investigation Agency, said China had left too many questions unanswered and that the smuggling of ivory was out of control.

It said that more than 20,000 elephants a year are killed illegally in Africa and Asia for the ivory black market, with Chinese nationals implicated in illegal ivory seizures in more than 20 African nations.

Five years ago, the Chinese government confessed to the convention that it had lost track of 121 tons of ivory - the equivalent to the tusks from 11,000 dead elephants - between 1991 and 2002 and indicated that it probably was sold on illegal markets.

But since then Beijing has tightened its surveillance. Chinese law provides for capital punishment and life imprisonment for smugglers.

The South African environment ministry said it was satisfied that both China and Japan have computerized systems to register tusks and ivory products, as well as strict controls and ivory detection equipment at ports of entry and exit to prevent illegal exports.

After the sale, South Africa and its neighbors will not be allowed to export ivory again for nine years and must use the sale proceeds for programs to protect their elephant populations.

Even though the elephant is classed as "vulnerable" at international level, South Africa's elephant population of 20,000 is set to double by 2020, placing a heavy toll on the balance of nature in the Kruger National Park and other wildlife centers.

The government last year warned that it would have to resume killing elephants - banned since 1995 - as a last resort measure to try to control the population explosion.